350-501 Question #393: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. The service provider is serving hosts with two different multicast streams from source X and source Y. Source X is multicast group 224.0.0.0/8, and source Y is multicast group 226.0.0.0/8. Multicast source X should send its stream through bidirectional RP address 10.20.1.1, and multicast source Y should send its stream through RP address 10.20.2.1. Which configuration meets these requirements?

Options

• AEnable ip pim ssm default on RA and RB.
• BAdd ip pim bidir-enable in global mode on RB.
• CPermit the source X and source Y IP addresses in the access list on RB.
• DSet PIM sparse mode with a static RP address of 10.20.2.1 on RA and RC.

Explanation

The network needs to support bidirectional PIM for Source X using RP 10.20.1.1 and regular PIM Sparse Mode for Source Y using RP 10.20.2.1. Enabling ip pim bidir-enable on RB allows it to participate in or act as a Bidirectional PIM router, which is crucial for the first requirement.

Common mistakes.

• A. Enabling ip pim ssm default configures Source Specific Multicast, which uses (S,G) channels and does not involve RPs or bidirectional PIM functionality.
• C. Permitting source IP addresses in an access list is typically used for defining valid sources or for RP-group mappings, but it does not enable bidirectional PIM itself.
• D. Setting PIM sparse mode with a static RP for 10.20.2.1 on RA and RC addresses the second requirement for Source Y but does not enable bidirectional PIM for Source X.

Concept tested. PIM Bidirectional (Bi-dir) configuration

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti/command/imc-cr-book/imc-i2.html#wp2506240228

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